Module 9 Sedimentary Rocks · on Clast Size, Shape, Sorting, and Composition Close to source Far...
Transcript of Module 9 Sedimentary Rocks · on Clast Size, Shape, Sorting, and Composition Close to source Far...
Rocks formed from material derived from Rocks formed from material derived from preexisting rocks by preexisting rocks by surfacialsurfacial processes processes followed by followed by diagenesisdiagenesis
There are two main classes of sedimentary rocksThere are two main classes of sedimentary rocksClasticClastic ((detritaldetrital) sedimentary rocks) sedimentary rocksare formed from bits and pieces of previously are formed from bits and pieces of previously existing rocks, called existing rocks, called clastsclasts or detritusor detritusChemical sedimentary rocksChemical sedimentary rocksare formed in several waysare formed in several ways
By precipitation from aqueous solutionBy precipitation from aqueous solutionFrom plant materialFrom plant materialFrom animal materialFrom animal material
SEDIMENTARY ROCKSSEDIMENTARY ROCKS
Processes Leading to Formation of Processes Leading to Formation of Clastic Sedimentary RocksClastic Sedimentary Rocks
ClasticClastic Sedimentary RocksSedimentary Rocks
Weathering:Weathering: the processes that change rocksthe processes that change rocks’’ size and size and composition at or near Earthcomposition at or near Earth’’s surfaces surfaceErosion and Transportation:Erosion and Transportation: removal of rock particles removal of rock particles (clasts) from their source by water, wind, or glacial ice(clasts) from their source by water, wind, or glacial iceDeposition:Deposition: the settling of clasts on Earththe settling of clasts on Earth’’s surface as s surface as sediments, leads to formation of a sedimentary bedsediments, leads to formation of a sedimentary bedCompaction:Compaction: pressing together of clasts, squeezing out pressing together of clasts, squeezing out pore water, by pressure exerted by overlying bedspore water, by pressure exerted by overlying bedsLithificationLithification:: cementation of clasts together to form a cementation of clasts together to form a sedimentary rocksedimentary rockDiagenesisDiagenesis:: a process of conversion of unconsolidated a process of conversion of unconsolidated sediments to coherent sedimentary rockssediments to coherent sedimentary rocks
Formation of Metamorphic RocksFormation of Metamorphic RocksUplift and exposure
Weathering
Transportation
Deposition
Compaction andLithification
All rocks exposed All rocks exposed at earthat earth’’s surface s surface undergoundergo……
Rocks CycleRocks Cycle
Tem
pera
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dec
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SiO
2of
liqu
id in
crea
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Olivine
Pyroxene
Amphibole
Biotite
Ca-rich
Na-rich
Ca-Na-rich
Na-Ca-rich
Quartz
Mus
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K-fe
ldsp
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Plag
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feld
spar
Dis
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Con
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BOWEN’S REACTION SERIES
Resistance of Minerals to WeatheringResistance of Minerals to Weathering
Most readilyto weathering
More resistant to weathering
Most resistant to weathering
Most resistant ofall to weathering
the effect of mineral compositionthe effect of mineral compositionon the resistance to weatheringon the resistance to weathering
Effect of Weathering, Gradient, Distance from SourceEffect of Weathering, Gradient, Distance from Source--Rock Rock on Clast Size, Shape, Sorting, and Compositionon Clast Size, Shape, Sorting, and Composition
Close to source Far from source
clast size large clasts small clasts
clast shape angular clasts rounded clasts
sorting poorly sorted sediments
well sorted sediments
composition rich in mafic mineralsand feldspar
quartz sands and clays
07_18.jpgEffect of Weathering, Gradient, Distance from SourceEffect of Weathering, Gradient, Distance from Source--Rock Rock on Clast Size, Shape, Sorting, and Compositionon Clast Size, Shape, Sorting, and Composition
Effects of Compaction, Cementation on SedimentsEffects of Compaction, Cementation on Sediments
On mudOn poorly-sorted
sediments
On well-sorted sediments
From sediments to sedimentary rocksFrom sediments to sedimentary rocks
clayclaysiltsiltsandsandgravelgravel
conglomerateconglomerate sandstonesandstone siltstonesiltstone claystoneclaystone
Clastic Sedimentary RockClastic Sedimentary Rock’’s Textures Texture
TextureTexture::the relationship between the grains of mineralsthe relationship between the grains of mineralsforming a rockforming a rock
a.a. grain sizegrain sizeb.b. roundnessroundnessc.c. sortingsortingd.d. fabricfabrice.e. ffragmenragment, matrix, & cementt, matrix, & cement
Clastic Sedimentary RockClastic Sedimentary Rock’’s Textures Texture
a.a. Grain size:Grain size:•• Grain (Grain (particleparticle,, clastclast,, fragmentfragment) size) size is is primary primary
distinguishing factordistinguishing factor for clastic sedimentary for clastic sedimentary rocksrocks
•• Size means diameter of rockSize means diameter of rock’’s grainss grains
Clastic Sedimentary RockClastic Sedimentary Rock’’s Textures TextureSizeSize (mm)(mm) Sedimentary clastsSedimentary clasts Sedimentary rocksSedimentary rocks
>256>256128 128 –– 25625664 64 –– 12812832 32 –– 646416 16 –– 32328 8 –– 16164 4 –– 882 2 –– 441 1 –– 22
1/2 1/2 –– 111/4 1/4 –– 1/21/21/8 1/8 –– 1/41/41/16 1/16 –– 1/81/81/32 1/32 –– 1/161/161/64 1/64 –– 1/321/32
1/128 1/128 –– 1/641/641/256 1/256 –– 1/1281/128
<1/256<1/256
•• BoulderBoulder•• CobbleCobble•• CobbleCobble•• PebblePebble•• PebblePebble•• PebblePebble•• PebblePebble•• GranuleGranule•• SandSand•• SandSand•• SandSand•• SandSand•• SandSand•• SiltSilt•• SiltSilt•• SiltSilt•• SiltSilt•• ClayClay
•• ––•• CoarseCoarse--•• FineFine--•• Very coarseVery coarse--•• CoarseCoarse--•• FineFine--•• Very fineVery fine--•• ––•• Very coarseVery coarse--•• CoarseCoarse•• MediumMedium--•• Fine_Fine_•• Very fineVery fine•• Very coarseVery coarse--•• CoarseCoarse•• FineFine--•• Very fineVery fine•• ––
Conglomerate (predominantlyConglomerate (predominantlyrounded rounded clastsclasts))or or BrecciaBreccia (predominantly(predominantlyAngular Angular clastsclasts))
SandstoneSandstone
SiltstoneSiltstone
ClaystoneClaystone or Shaleor Shale
MudstoneMudstone
WentworthWentworth’’ ScaleScale
Clastic Sedimentary RockClastic Sedimentary Rock’’s Textures Texture
b. b. SphericitySphericity vsvs roundnessroundness•• SphericitySphericity is a degree of similarity to a ball is a degree of similarity to a ball
shapeshape•• Roundness is a degree of roundedness of the Roundness is a degree of roundedness of the
edges of a fragmentedges of a fragment
angularangular intermediateintermediate roundedrounded
High High sphericitysphericity
Low Low sphericitysphericity
RoundnessRoundness
Clastic Sedimentary RockClastic Sedimentary Rock’’s Textures Texture
c. Sortingc. Sorting•• Degree of similarity in particle sizeDegree of similarity in particle size
Clastic Sedimentary RockClastic Sedimentary Rock’’s Textures Texture
This quartz grains are:This quartz grains are:-well-sorted-well-rounded
d. Fabricd. Fabric•• Opened fabricOpened fabric•• Closed fabricClosed fabric
Clastic Sedimentary RockClastic Sedimentary Rock’’s Textures Texture
Closed fabricClosed fabric
Opened fabricOpened fabric
Clastic Sedimentary RockClastic Sedimentary Rock’’s Textures Texture
e. Fragments, matrix, cemente. Fragments, matrix, cement•• Fragments (Fragments (clastsclasts))•• MatrixMatrix•• CementCement
The Most Common Sedimentary CementsThe Most Common Sedimentary CementsClastic Sedimentary RockClastic Sedimentary Rock’’s Textures Texture
•• CalciteCalcite–– The most common cement present in marine sedimentary The most common cement present in marine sedimentary
rocksrocks–– Also common in sedimentary rocks formed from sediments Also common in sedimentary rocks formed from sediments
deposited in evaporite basinsdeposited in evaporite basins–– Calcite cemented sedimentary rocks give a positive acid Calcite cemented sedimentary rocks give a positive acid
test (will fizz when an acidic solution is dropped on them)test (will fizz when an acidic solution is dropped on them)
•• HematiteHematite–– The cement present in red colored terrigenous (landThe cement present in red colored terrigenous (land--
derived) sedimentary rocks, very commonderived) sedimentary rocks, very common–– Hematite cemented rocks will not fizz when an acidic Hematite cemented rocks will not fizz when an acidic
solution is dropped on themsolution is dropped on them
•• SilicaSilica–– The cement present in terrigenous (landThe cement present in terrigenous (land--derived) derived)
sedimentary rocks that are not red, very commonsedimentary rocks that are not red, very common–– Silica cemented rocks will not fizz when an acidic solution is Silica cemented rocks will not fizz when an acidic solution is
dropped on themdropped on them
Clastic Sedimentary RockClastic Sedimentary Rock’’s Structures Structure
Sedimentary Beds and Bedding PlanesSedimentary Beds and Bedding PlanesBeds represent distinct sedimentary event, Beds represent distinct sedimentary event, times when deposition occurredtimes when deposition occurredBedding planes represent pauses between Bedding planes represent pauses between sedimentary events, times when deposition ceasedsedimentary events, times when deposition ceased
Beddingplane
Bed
Clastic Sedimentary RockClastic Sedimentary Rock’’s Structures Structure
Graded Sedimentary BedsGraded Sedimentary BedsForm in response to Form in response to decrease in energy decrease in energy during depositionduring depositionLarger, heavier clastsLarger, heavier clasts, , first pebbles then sand, first pebbles then sand, settle out first, in the settle out first, in the bottom of the bedbottom of the bedSmaller, lighter clastsSmaller, lighter clasts, , silt and finally clay, silt and finally clay, settle out last in the top settle out last in the top of the bedof the bed
Clastic Sedimentary RockClastic Sedimentary Rock’’s Structures Structure
Cross Beds Cross Beds Cross beds are Cross beds are deposited in response deposited in response to movement of a to movement of a currentcurrent
Cross beds are Cross beds are unidirectional if the unidirectional if the current was constant current was constant in directionin direction
Cross beds are biCross beds are bi--directional if the directional if the current was not current was not constant in directionconstant in direction
Note: these beds are Note: these beds are tilted
Current direction
tilted
Mud CracksMud CracksMud cracks form Mud cracks form when mud dries when mud dries upup
Their shape and Their shape and size may vary size may vary considerablyconsiderably
Mudcracks in fresh sediment
Mudcracks Mudcracks in a in a
sedimentary sedimentary rockrock
Clastic Sedimentary RockClastic Sedimentary Rock’’s Structures Structure
Clastic Sedimentary RockClastic Sedimentary Rock’’s Structures StructureRipple Marks Ripple Marks
Are formed in response to Are formed in response to movement of a currentmovement of a current
Symmetrical ripple marksSymmetrical ripple marksform if current is backform if current is back--andand--forth, biforth, bi--directionaldirectional
Asymmetrical ripple marksAsymmetrical ripple marksform if current is constant in form if current is constant in directiondirection
Asymmetrical ripple marks in fresh sediment
Symmetrical ripple marks preserved in mudstone
Raindrop Imprints and castsRaindrop Imprints and castsForm when big rain drops fall on mudForm when big rain drops fall on mudRaindrop imprintsRaindrop imprints are depressions formed on the are depressions formed on the bed upon which the raindrops fellbed upon which the raindrops fellRaindrop castsRaindrop casts are knobs formed on the bottom of are knobs formed on the bottom of the bed deposited on top of the bed upon which the the bed deposited on top of the bed upon which the raindrops fellraindrops fell
Raindrop imprints and mudcracks
Clastic Sedimentary RockClastic Sedimentary Rock’’s Structures Structure
Clastic Sedimentary RockClastic Sedimentary Rock’’s Structures StructureFossilsFossils
Are any evidence of life preserved in ancient rocksAre any evidence of life preserved in ancient rocksInclude bones, teeth, shells, molds and casts, Include bones, teeth, shells, molds and casts, petrified wood, impressions, footprints, etc.petrified wood, impressions, footprints, etc.
Chemical Sedimentary RocksChemical Sedimentary Rocks
Chemical Sedimentary RocksChemical Sedimentary Rocksderived from material carried derived from material carried in solutionin solution to to lakes/ seaslakes/ seasprecipitationprecipitation from solution to form from solution to form ““chemical sedimentschemical sediments””
by precipitation from aqueous solutionby precipitation from aqueous solutionfrom plant material from plant material from animal materialfrom animal material
Salt flats, UtahSalt flats, Utah
Chemical Sedimentary RocksChemical Sedimentary Rocks
EvaporitesEvaporiteswater evaporates and water evaporates and dissolved stuff is dissolved stuff is depositeddepositedmostly marine rocks, mostly marine rocks, but some lakes/ playasbut some lakes/ playasSalt, gypsum, potashSalt, gypsum, potash
Death Valley, CaliforniaDeath Valley, California
T&L Fig 6.12
Chemical Sedimentary RocksChemical Sedimentary Rocks
ChertChertvery fine grained silicavery fine grained silicaalso called flint, jasper, also called flint, jasper, agateagatemost formed in oceanmost formed in oceanoccurs as layers (beds) occurs as layers (beds) & as irregular blobs in & as irregular blobs in limestonelimestonemarine creatures marine creatures remove silica from sea remove silica from sea water, make shellswater, make shells
AgateAgate
LimestoneLimestoneformed by marine organisms formed by marine organisms (corals, clams, algae)(corals, clams, algae)composed primarily of calcite composed primarily of calcite (calcium carbonate CaCO3)(calcium carbonate CaCO3)most abundant chemical most abundant chemical sedimentary rocksedimentary rock10% of all sedimentary rocks 10% of all sedimentary rocks (by volume)(by volume)some deposited directly out of some deposited directly out of ocean or other watersocean or other waters
Chemical Sedimentary RocksChemical Sedimentary Rocks
Coral reefCoral reef
Coquina (rock of shell fragments)Coquina (rock of shell fragments)
Coal
Chemical Sedimentary RocksChemical Sedimentary Rocks
CoalCoalburied and compacted plant materialburied and compacted plant materialdifferent kinds of coal, depending on formation different kinds of coal, depending on formation process process
peatpeat lignitelignite coalcoal anthraciteanthracite
Classification of Sedimentary RocksClassification of Sedimentary RocksC
last
icC
last
icSe
dim
enta
ry R
ocks
Sedi
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tary
Roc
ksC
hem
ical
Che
mic
alSe
dim
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ocks
Sedi
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tary
Roc
ks
ChertChert RadiolariteRadiolariteDiatomiteDiatomite
SILICASILICAPeatPeat
LigniteLigniteCoalCoal
AnthraciteAnthracite
CARBONACEOUSCARBONACEOUS
HaliteHaliteGypsumGypsum
AnhydriteAnhydrite
EVAPORITEEVAPORITE
OoliteOolite
Coral limestoneCoral limestoneDolomiteDolomiteCrystalline limestone Crystalline limestone
BioclasticBioclastic limestone limestone
Marl; Marl; ClasticClastic limestonelimestone((CalcaruditeCalcarudite, , CalcareniteCalcarenite, , CalcelutiteCalcelutite))
CARBONATECARBONATE
SILICATESILICATEBrecciaBreccia SiltstoneSiltstoneConglomerate Conglomerate ClaystoneClaystoneSandstone ShaleSandstone Shale
CLASTICCLASTIC
ANORGANICANORGANIC ORGANICORGANIC
Chemical Sedimentary Rocks:Chemical Sedimentary Rocks:Formed by Precipitation from Aqueous SolutionFormed by Precipitation from Aqueous Solution
1. The Evaporites1. The Evaporites
a. Halite (NaCl)
b. Calcite (CaCO3)
c. Gypsum (CaSO4. H2O)
2. Precipitated Silica2. Precipitated Silica
Chert
Chemical Sedimentary Rocks:Formed from Plant Material
Chemical Sedimentary Rocks:Chemical Sedimentary Rocks:Formed from Plants Material: The CoalFormed from Plants Material: The Coal
Inundatedswamp or
marshBituminous coalBituminous coal
(soft coal)(soft coal)PeatPeat LigniteLignite
Coal seams in Mesa Verde National ParkCoal seams in Mesa Verde National Park Bituminous coalBituminous coal
Chemical Sedimentary Rocks:Chemical Sedimentary Rocks:Formed from Animal Material: The LimestonesFormed from Animal Material: The Limestones
1. Limestone (a limey mudstone)
All contain CaCOAll contain CaCO3 All will fizz in contact with acidAll will fizz in contact with acid3
2. Fossiliferous limestone
3. Coquina
4. Chalk